feat: add swift implementation to lcp problem: No.18

Author: klever34

lcp/LCP 18. 早餐组合/README.md

@@ -187,6 +187,37 @@ func breakfastNumber(staple []int, drinks []int, x int) int {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func breakfastNumber(_ staple: [Int], _ drinks: [Int], _ x: Int) -> Int {
+        let mod = 1000000007
+        var result = 0
+        let sortedDrinks = drinks.sorted()
+        
+        for s in staple {
+            let remaining = x - s
+            if remaining >= sortedDrinks.first ?? 0 {
+                var left = 0
+                var right = sortedDrinks.count - 1
+                
+                while left < right {
+                    let mid = (left + right + 1) / 2
+                    if sortedDrinks[mid] <= remaining {
+                        left = mid
+                    } else {
+                        right = mid - 1
+                    }
+                }
+                result = (result + left + 1) % mod
+            }
+        }
+        return result
+    }
+}
+```
+
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 <!-- solution:end -->